1. Field of the Invention
This invention relates to a high precision gantry machine providing precise movement of a tool in two perpendicular directions over a workpiece.
2. Description of Related Art
Powerful and accurate Cartesian gantry systems are known. They are found in production plants around the world in applications including high-speed pick-and-place machines, accurate assembly machines, vision inspection machines, dispensing stations and high-accuracy scribing stations, for example. Typically, two parallel Y-direction tracks, and at least one Y-direction stage provide Y-direction motion to a bridge that supports an X-direction track which provides X-direction motion to a tool or other device. Thus, the X and Y position of the tool can be established over a workpiece. The Y-direction tracks are fixed relative to a unitary base, for example, a large block of granite or other material. As the ambient temperature of the gantry system changes, there can be a differential thermal expansion or contraction between the base and the bridge which can result in forces between the bridge and the Y-direction stage which, in turn, can place elements of the gantry system out of alignment or cause a change in running friction resulting in a degradation in system performance. The ambient temperature change can result due to changing work environment conditions at the time of shipping, or even as a result of heating of the bridge during use due to the motors it supports.
Compliant mounts or flexures for absorbing stresses due to thermal expansion have been used in the past as shown, for example, in U.S. Pat. No. 6,019,514 and U.S. Pat. No. 6,058,618. For high-precision gantry systems, the assignee of this application has incorporated flexure plates with spaced flexure sections joined to central and outer sections. The outer sections are fixed to either a Y-direction stage or the bridge and the central section is connected to the other of the Y-direction stage and the bridge.
The longer the bridge of a gantry system, the more important it is to provide additional support to prevent rotation or twisting about the longitudinal axis of the bridge. It is an object of this invention to provide such additional support against rotation and twisting without interfering with the functioning of the flexure plates.